Part 3: Aerodynamic drag of the Superman position (which cyclist hill descent position is really superior?)

We have received a fairly large number of requests from readers to comment on You Tube movies and other movies of a cyclist in a rather peculiar position, referred to as the "Superman" position (see Figure 1).

Figure 1: "Superman" position for hill descent. Source: You Tube.

To honor these requests, we have analyzed the aerodynamic drag of this position with Computational Fluid Dynamics simulations with the ANSYS Fluent CFD code. Simulation settings and parameters were similar to those in our earlier post, where we also compared simulation results with wind tunnel measurements:

The results of the previous study along with those of the "Superman" position study are summarized in Figure 2.

Figure 2: Relative comparison of different hill descent positions in terms of speed (no pedaling).

One might wonder why this position with the cyclist body stretched out fairly horizontally is only 7% faster than the "Top tube safe" position. The answer is the bicycle. For the "Top tube safe" position, the aerodynamic drag of the cyclist body is about 74% of the total drag and that of the bicycle about 26% of the total drag. For the "Superman" position, these percentages are 61% and 39%. The more aerodynamic the position of the cyclist body, the larger the relative contribution of the bicycle to the overall drag. However, the bicycle drag does not change substantially (apart from interference effects) so increasingly aerodynamic positions of the cyclist body are faced with the asymptote/ultimate limit of the bicycle drag.

Evidently, pedaling is not possible in this "Superman" position and this position is dangerous and irresponsible. Professional and recreational cyclists are counteradvised to ever attempt this and the International Cycling Union should ban of this type of position by means of its rules. Cycling is already dangerous enough as it is, and cyclist safety should always be the top priority.

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